Arylamines are useful as hole transport compounds in electrophotographic imaging devices and processes, see, for example, U.S. Pat. No. 7,544,842, incorporated herein by reference in entirety. Dimethoxy tetraphenylbenzidine (also known as, for example, N,N′-diphenyl-N,N′-bis(3-methoxylphenyl)-[1,1′-biphenyl]-4,4′-diamine or N,N′-diphenyl-N,N′-bis(3-methoxylphenyl)-[4,4′-diaminobiphenyl]) is a precursor of the hole transport material, dihydroxy tetraphenylbenzidine (also known as N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-[1,1′-biphenyl]-4,4′-diamine), which is readily produced from dimethoxy tetraphenylbenzidine. Dihydroxy tetraphenylbenzidine can be used in one or more layers of photoreceptors, see, for example, U.S. Pat. No. 5,336,577 which teaches use of dihydroxy tetraphenyl benzidine in a single layer photoreceptor. Tetraphenyl benzidine-containing polymers are described in U.S. Pat. Nos. 4,801,517, 4,806,443, 4,806,444, 4,818,650, 4,871,634, 4,935,487, 4,956,440 and 5,028,687, the disclosures thereof are incorporated herein by reference in entirety.
Synthesis of arylamine hole transport compounds generally requires intermediates, some of which are costly and/or are time-consuming to produce, that are part of multi-step processes.
Buchwald chemistry can be used to produce arylamine compounds. The formation of diarylamines and triarylamines comprises an exothermic reaction of an arylamine with an aryl halide in the presence of a palladium catalyst and base.
Many of those synthesis methods are batch reactions. Because of the reaction conditions, scaling of batch Buchwald syntheses presents challenges, such as, accommodating the heat of reaction and batch workup delays.
A continuous process, if possible, provides advantages over more conventional batch reactions by providing one or more of faster efficient mixing, selectivity enhanced-side products, reduced secondary reactions, higher yield, fewer impurities, extreme reaction conditions, time and cost savings, and increased surface area to volume ratio that results in good mass and heat transfer.
Microreactors and minireactors for making particular arylamines under certain conditions have been described. However, the smaller bore fluid channels used therein may limit production, scaling and reaction efficiency. U.S. Pat. No. 7,563,932 describes a microreactor, and is incorporated herein by reference in entirety.
Continuous processes however, do have some shortcomings, for example, because of the need for reactant and product communication means, there is a risk of blocking such conduits with reactants and/or products. Hence, reactions that produce a solid product or side product, such as, solid halide salts, such as, sodium bromide, produced in a Buchwald reaction, may not be amenable to a continuous process.